Boiling point of water and extra energy

[nadia86]

ONce water has been heated to its boiling point additional heating will not raise its temperature. What happens to htis additional energy?

[New Judge]

It takes one calorie of heat to raise the temperature of one gram of water by one degree Celsius. However, once the water has reached its boiling point (100 C) it then takes a further 540 calories to convert each gram from its liquid state to its gaseous state. So that�s where some of the energy goes.

However, there is nothing to prevent the steam then generated having its temperature raised (steam is not limited to 100 C, only liquid water at normal pressure is). So if additional heat is applied to the steam that is generated its temperature will also rise. Of course you have to prevent the steam escaping. When you do, and you continue to heat it, the pressure within the containment vessel will rise, and this uses more of the energy.

Many commercial boilers generate �superheated� steam (that is, steam above 100 C) by routing it through the heat source that was used to boil the water. Superheated steam can provide greater mechanical energy than steam at 100 C.

If, on the other hand, you simply let the steam escape as you produce it, its energy (which is the energy you used to raise the temperature of the water and then vaporise it) will be lost to the surroundings.

[Teddio]

The additional energy breaks the intermolecular bonds between the water molecules. Work is done overcoming the forces of attraction between the molecules, this is considerable. 2.2 million joules of heat energy are needed to produce 1kg of steam at 100C from 1kg of water at 100C.